DESCRIPTION (Taken From the Applicant's Abstract) Reproductive toxicants have often been identified after-the-fact, from observations in affected groups of humans. As an example, in the 20th Century, a synthetic-estrogen, diethylstilbestrol, was found to cause malformations in the reproductive tracts of male and female offspring of women who had taken the drug during pregnancy to prevent miscarriage. Thus, effects that had been caused in utero in the reproductive tracts of both sons and daughters were not discovered for several decades. Due to examples like this, regulatory agencies now require extensive testing of chemicals for potential reproductive toxicities, and they are often forced to use default assumptions and err on the side of safety, in their recommendations. Therefore, it is critical to understand more completely at the cellular and molecular level, how xenobiotics can impact male and female reproductive systems. Additionally, this understanding will greatly benefit from direct comparisons of how similarities and differences between males and females dictate gender-specific responses to toxicant exposures. Therefore, a symposium on "Gender Differences in Reproductive Biology and Toxicology" is being planned for November 9-11, 2000, with the unique following Specific Aims: 1) to bring together a multi disciplinary group of biologists and toxicologists interested in male and female reproduction in order to facilitate their direct interactions and communications, 2) to discover and discuss gender similarities and differences in reproductive biology and toxicology at the cellular and molecular level, 3) to demonstrate how state-of-the-art technologies and animal models can be used to advance the understanding of gender differences in reproductive toxicology, and 4) to identify questions, gaps, and future directions the field should pursue. The proposed symposium proposes to provide a unique and timely opportunity for a specialized interdisciplinary group of researchers to develop a better understanding of gender-specific aspects of responses to reproductive toxicants. 150-200 participants are expected to attend the symposium. The outcome of this interaction proposes to impact the future direction of reproductive toxicology and enhance its application to environmental health in the 21st Century.